Treatment of ferrophos



ocf- 27 1964 w. l.. DARRow ETAL 3,154,410

TREATMENT oF FERRoPHos `Filed June 27. 1961 United States Patent 3,154,410 TREATMENT 0F FERRUPEKBS Wendell L. Darrow and Chao Haino, Alameda, idaho,

Alfred Gordon Evans Rohiette, Bovingdon Herts, England, and Blair Burweil, Grand function, Colo.; said Rohiette and said Burwell assignors to Minerals Engineering Company, Grand .lunctiom Colo., a company of Colorado, and said Darrow and said Hsiao assignors to FMC Corporation, a corporation of Delaware Filed .lune 27, 1961, Ser. No. 120,881 8 Claims. (Cl. 75-101) This invention relates to the processing of ferrophos, and particularly to the selective concentration and separation of vanadium and chromium present in ferrophos derived from phosphate ores.

This application is a continuation-impart of US. Serial No. 60,099, tiled October 3, 1960, now abandoned, by the present inventors and assigned to the present assignee.

There exist in the United States, and particularly in the western part of the United States, large deposits of phosphate rock, or ore, containing approximately 25% or more P205 in the form of dry calcium phosphate. The calcium content of this ore is about 30 to 50%, expressed as CaO. The ore also contains silica, iron oxide, organic matter and clay as well as small quantities of chromium oxide and vanadium oxide. The vanadium is present in the ore in the amount of about 0.05% to 1% as V205, depending on the location of the phosphate bed and the richness of the bed in phosphate minerals. The average vanadium content of the western ore is approximately 0.25% V205.

Conventionally, the ore is treated for the extraction of its contained phosphorus by smelting in an electric furnace with coke under reducing conditions, whereby the phosphorus is volatilized as elemental phosphorus and condensed and recovered. The iron oxide in the ore, together with the vanadium and chromium in it, is reduced to a metal alloy which contains about 24 to 28% phosphorus, 52 to 60% iron, 31/2 to 8% vanadium and 2 to 6% chromium.

The vanadium-bearing alloy, known as ferrophos, has found use in the iron industry, where it is employed as a source of high-phosphorus iron. However, in this market the valuable vanadium and chromium present in the alloy confer no advantage, and accordingly are wasted. Furthermore, the Vanadium and chromium Vary in concentration in the ferrophos, and this variability has been found to interfere seriously with the production of quality steel from the ferrophos.

It has long been desired to provide a method for providing a ferrophos which is free of excess vanadium and chromium, and yet which has a high and constant phosphorus content, such that the ferrophos is suitable directly for use in iron treatment. It has been desired also to provide a method for recovering the vanadium and chromium which is removed from the ferrophos, in a recovered form in which it is pure, and particularly in which it is substantially free of contaminating phosphorus. The presence of greater than about 0.05% of phosphorus in vanadium makes it unsuitable in such applications as vanadium-bearing steels.

In an attempt to accomplish the first of these desirable ends, namely, the removal of vanadium, and along with it chromium, from ferrophos, Kerschbaum devised a method of blowing the ferrophos with air in molten condition until the vanadium is substantially all oxidized. This method is taught in his U.S. Patent No. 2,467,039. While the Kerschbaum method operates to concentrate the vanadium, when the ferrophos is blown in molten condition with air or oxygen-enriched air without control of temperature until the vanadium is substantially com- 3, lSLlA l 0 Patented Get. 27, 1964 pletely oxidized, as taught by Kerschbaum, a large and variable amount of the phosphorus also is volatilized and oxidized, and a residual ferrophos having a low phosphorus content, about 20% or even less, and furthermore having a phosphorus content which varies considerably from batch to batch, is produced. This variability is of of serious disadvantage in steel production because the phosphorus content of the steel produced from the ferrophos must be controlled closely. To adjust for the variations in the ferrophos make-up, a complicated and expensive control system must be resorted to.

The absence of a satisfactory process for upgrading ferrophos and simultaneously producing a useful concentrate of vanadium, has hindered development of the second desirable end, recovery of the excess vanadium and chromium from the ferrophos in a form in which it is substantially free of phosphorus. Despite this, the demand for vanadium has been great enough to cause workers to attempt to recover vanadium directly from select portions of phosphate ore, namely, those which contain about 1% of vanadium or more. One attempt has involved oxidatively roasting the ore with sodium carbonate and/or sodium chloride at high temperatures. This method has met with little success, because of the high organic content of the ores, and because of their high lime, that is calcium oxide, contents. Furthermore, because of these di'lliculties, it has not been possible to recognize the problems involved in recovery of vanadium from a ferrophos-derived concentrate.

It is a feature of the present invention to provide a method of concentrating and extracting vanadium and chromium present in ferrophos, whereby a residual ferrophos having a high and constant phosphorus content is produced.

It is a further feature of this invention to provide an eiiicient method of separating a major portion of the Vanadium present in the concentrate, in a form in which it contains minimal amounts of phosphorus.

It has now been found that if ferrophos is heated in molten condition in an oxidizing atmosphere with careful control of the temperature of the molten reaction mixture from about 1300 C. at which the reaction proceeds slowly, to a maximum of l560 C. above which temperature phosphorus is rapidly lost, and preferably to about l400 to l500 C., a concentrate rich in vanadium and chromium is formed, which can be separated readily in molten or solid form from the residual ferrophos, while the phosphorus in the ferrophos is not volatilized substantially, and accordingly little phosphorus is lost overhead as vapor. This avoidance of phosphorus loss means that the phosphorus content of the residual ferrophos is controlled at a high level, and, since the amount which goes into the concentrate may likewise be controlled readily, the amount of phosphorus in the residual ferrophos is maintained within close limits. It has been found that the phosphorus content of the residual ferrophos can be consistently maintained at any desired level of on the order of 23% or even higher. This is of particular signilicance since a ferrophos having a phosphorus content which is substantially below about 23%, or which varies substantially from batch to batch, has been found to cause major operating problems in steel manufacture.

It has also been discovered that a particularly pure water solution of sodium vanadfate, having a phosphorus content of only about 0.1 to 0.3% or less, and from which essentially pure vanadium can be recovered by known means, can be produced from a ferrophos-derived concentrate rich in vanadium made as described above, by roasting the concentrate at about 600 to 800 C. for about 1/2 to 2 hours in the presence of sodium chloride, provided the calcium content of the concentrate is less than about 5%, expressed as calcium oxide. The concentrate, which typically contains about 10 to 15% of vanadium oxide, 8 to 12% of chromium oxide, on the order of 40% of phosphorus as P205, less than 5% of CaO, and the balance iron oxide and silica, is mixed in particulate form with sodium chloride, and the mix is roasted in an oxidizing atmosphere at the indicated temperature land for the indicated time. Sodium chloride is used in an amount which varies depending on the amount of vanadium, iron, silica, and other constituents which react with the salt in roasting, and preferably is adjusted so that the amount of excess salt present after the roasting step is about 1 to 3 times the amount of vanadium oxide.

The present controlled sodium chloride roast selecing only very small amounts of other elements such as phosphorus. Aqueous solutions of sodium vanadate containing less than about 0.1%, that is less than about 1 gram per liter, of phosphorus as P205 can be treated by known means, described hereinafter, to produce high yields of vanadium having present as an impurity less than about 0.05% of phosphorus. Sodium vanadate solutions containing more than about 0.1% of phosphorus as P205, or less than about 1% of vanadium as V205 will not produce high vanadium yields, and therefore it is preferred to have present in the solution to be treated less than about 0.1% of phosphorus as P205, and more than 1% of vanadium as V205. The solutions can be adjusted in P205 and V205 contents by dilution with water, concentration, and the like to provide the preferred amounts of phosphorus and vanadium.

The high purity of the vanadium produced by the present process is surprising, in view of the fact that similar treatment of a concentrate with other sodium salts such as sodium carbonate, or roasting of a concentrate at a temperature of greater than 800 C. for an extended time, or roasting of a concentrate containing more than 5% of calcuim as calcium oxide even with sodium chloride or sodium carbonate, produces mixtures of water-soluble derivatives of vanadium containing substantial amounts of phosphorus and other components of the ferrophos. Recovery of pure vanadium from these mixtures is not commercially practical. Y

The present invention will now be described more fully with reference to the single attached drawing, in which is a reaction furnace into which ferrophos feed 12 and air 14 are introduced. The ferrophos preferably is introduced in solid form and melted initially by heat derived from burning coke or other fuel 16, although it may be introduced in molten form. In either case, air is blown through the molten ferrophos, and the exothermal oxidation reaction provides suflicient heat to continue the oxidation.

A vanadium-rich concentrate rises to the surface of the melted ferrophos, and overflows through line 18 either to collection tank 20 or pulverizer 22. The residual ferrophos is recovered through line 24. In some cases the mix is turbulent, and the concentrate will not rise to the surface. In this case, the mix is permitted to cool in quiescent condition, for example, in a second vessel, whereupon the concentrate does rise to the surface. It then can be separated from the remainder of the batch, either in liquid or cooled, solid state.

The concentrate at this point contains about 10 to of vanadium as V205 8 to 12% of chromium as Cr203, about 40% of phosphorus as P205, and the balance principally iron oxides, with silica and calcium being present in small amounts. The calcium content of the ferrophos is maintained, by means described hereinafter, below about 5%, in order to facilitate subsequent separation of vanadium from the concentrate. The residual ferrophos contains at least about 23% of phosphorus, a condition in which it is highly useful in steel manufacture. Further, the over-all phosphorus and iron losses in the concentration are low, and the high yields make for economical operation.

The concentrate may then be passed to pulverizer 22 where it is ground to particles which are moved through line 26 to roaster 28 where they are mixed with sodium chloride particles and roasted at a temperature of abo-ut 600 to 800C. for about 1/2 to 2 hours. The roasted particles are then passed through line 30 to dissolver 32, where they are leached with water to selectively leach and remove the soluble sodium vanadate formed in roaster 28. The resulting water solution of sodium vanadate is removed through line 34 for sale or further processing to provide other Vanadium derivatives, while the vanadium-depleted concentrate is removed through line 36, and the phosphorus, iron :and other ingredients in it are recovered. ferrophos operation'.Y

Ferrophos obtained from western United States phosphate ores is preferred for use in the present process. This particular ore contains a large amount of vanadium, as much as about 1% as V205, and accordingly its recovery is economically attractive. However, ferrophos derived from ores containing less vanadium may be processed by the present method, lalthough it will be apparent that the smaller vanadium content of other ores reduces the economic attractiveness of the process. The western ores likewise contain large amounts of chromium, making its recovery also attractive.

It is important to the subsequent recovery of the vanadium, that less than about 5% of calcium as calcium oxide be present in the ferrophos, and in the concentrate. The calcium content can be controlled at the desired level, for example but not exclusively, by providing at least about 5% of silica as Si02 in the ore which is being processed to proved the ferrophos. The Si02 reacts during processing with the calcium to form calcium silicate, which slags out from the ferrophos.

The concentrate is formed by heating the ferrophos in molten condition under oxidizing conditions, in typical oxidation equipment such as la Bessemer converter or any other suitable reaction vessel designed to operate at the required temperatures and under the otherv conditions defined herein. passing air or oxygen-enriched air through the molten bath of ferrophos, while the temperature of the oxidation is controlled carefully to from about 1300 to ya maximum of 1560C. and preferably between 1400 to 1500C. At temperatures below about 1300C. the burden in the reactor is highly viscous and the required separation of concentrate from the ferrophos does not occur. At temperatures above 1560C., an undue amount of phosphorus is volatilized and lost overhead. This means that control of the proportion of phosphorus to iron in the residual ferrophos is diflicult, and furthermore that the amount of phosphorus in the ferrophos is reduced to van undesirable extent.

The oxidation is an exothermic reaction, and therefore it is necessary to provide for control of the temperature by means such as return of solid ferrophos or other ironcontaining agents such as cast iron, magnetite and the'like, to the molten bath, or other obvious cooling means such as external water cooling. If the temperature is not controlled, it will rise to above about 1600 C., and the advantages of the present process will be lost. At temperatures above about 1600 C., an excessive amount of phosphorus is volatilized and lost. The temperatures of the mixture is measured at the bottom tap hole, for example, with an optical pyrometer, for the reasony that the batch is highly corrosive to temperature measuring means placed within it. Furthermore, the presence of phosphorus vapors over the molten batch renders optical measurements from above impractical.

The oxidation is preferably continued until at least about 50%, but no more than about 95%, of the vanadium in the ferrophos is converted to vanadium oxide and no more than about 1% of vanadium remains in the residue. Economically, it is not desirable to leave more than this amount of vanadium in the ferrophos as it is not If desired,they :can be refed to the i The oxidation is conducted by useful in the ferrophos and therefore confers no economic advantage. It also is not suitable to convert more than about 95% of the vanadium to its oxide, as in converting the remainder above the 95% level, an undue amount of phosphorus and iron may be oxidized and lost.

The concentrate may be removed readily from the oxidation furnace by tapping or skimming, although any means of separating it from the ferrophos may be employed. The separated concentrate is then converted to particulate form, to provide particles which will pass through a 60 mesh screen. Use of coarser particles reduces reaction efiiciency, while use of liner particles results in more efficient reaction. The particles are mixed with sufficient sodium chloride to react with all of the vanadium, iron, silica and other constituents which reacts with the salt in roasting, and preferably to provide that the amount of unreacted salt after roasting is about 1 to 3 times the amount of vanadium oxide. lt is critical, however, only that sufficient salt be present to react with all of the reactive ingredients in the concentrate. The mixture is roasted under oxidizing conditions, that is, in the presence of oxygen-enriched air, or air at about 600 to 800 C. The roast should not be continued for more than about 1 to 2 hours, for the reason that roasting for an excessive time even at this controlled temperature results in oxidation of some phosphorus, and therefore in greatly reducing the value of the vanadium oxide recovered.

The roast selectively converts the vanadium present in the concentrate to water-soluble form as sodium vanadate, Na/207, by leaving the other components of the concentrate behind in insoluble form. lt has been found that if less than about 0.1% of phosphorus, as P205, is present in the aqueous sodium vanadate solution, elemental vanadium can readily be recovered, containing less than about 0.05% phosphorus. This control of phosphorus is readily achieved by the present controlled roasting method.

Typical known methods of recovering the vanadium from its solution as sodium vanadate provide it in the form of ammonium metavanadate, vanadium oxide, ferrovanadium, and the like. It is of interest that when other sodium salts are employed in the roast in place of sodium chloride, a large amount of phosphorus as well as vanadium is converted to soluble form, and separation of the vanadium as an essentially phosphorus-free product is difficult, if not impossible economically. Furthermore, when the roast is conducted at an unduly high temperature and for a long time, for example, at 820 C. for

2 hours, even with sodium chloride as the roasting material, the solution resulting from the roast and subsequent dissolution of the soluble oxidized products contains an excessive amount of phosphorus as P205. This means that when the solution is subsequently treated to precipitate vanadium oxide, the oxide recovered contains greater than on the order of 0.05 phosphorus, and therefore is not useable in many applications.

Where the vanadium is present in the concentrate in a large amount, for example, in the amount of about 8 to 10%, it may be desirable to conduct the roast in steps to avoid over-concentration of sodium vanadate in the roaster. This product melts at the roasting temperature and is apt to cause agglomeration of the particles. Stepwise roasting is not necessary although it will be apparent that it is desirable for ease of operation, It is preferred to operate a sodium chloride roast for about one hour at 600 to 700 C. If the roast is carried out at a temperature substantially higher than 800 C., as indicated above, or for too long a time, the solubilization of the vanadium is not selective and the process loses a major part of its value.

In order to remove the sodium vanadate from the roasted concentrate, the concentrate is mixed with water and the soluble vanadium separated from the insoluble residue by decantation or filtration. The vanadium in the separated solution is then recovered, for example, as red cake, that is, an impure oxide of Vanadium, by acidifying the solution to a pH of about 4 and boiling to form a hydrated insoluble NazVqOGXHzO, which usually contains about 86% of V205, and is sold after fusion as a product known in the trade as fuse vanadium oxide. If desired, the vanadium can be precipitated as ammonium metavanadate, which upon heating forms pure V205 having an assay of about 98 to 99%.

it should be noted also that the use of sodium chloride in the present roast process has the added advantage that it results in the formation of chlorine gas and hydrochloric acid at temperatures of about 650 C. or more, according to the following reaction:

The chlorine gas is readily recovered by scrubbing the gases evolved from the roaster with ammonia solutions by well-known methods to form an ammonium chloride solution. These solutions can be employed in recovering vanadium from its solutions as ammonium metavanadate.

Concentrates produced from ferrophos by methods other than the above method, for example, by the method of Kerschbaum or other ferrophos treatments, can be employed with the above roasting process to provide vanadium products. It is important only that the concentrate contain a minimum of about 1% of vanadium as V205, and that calcium be present in the concentrate in an amount less than about 5%, calculated as calcium oxide.

The following examples are presented by way of illustration only, and are not intended to limit the scope of the present invention in any way.

CONCENTRATION OF VANADIUM IN FERROPHOS Example 1 PRESENT METHOD, BATCH PROCESS Four hundred and forty-tive pounds of ferrophos containing 27.6% phosphorus, 5.05% vanadium, 4.9% chromium, 59.5% iron, and 2% of calcium, was melted by burning with coke for twenty minutes, and blown with air in a converter 15 inches in diameter and 6 feet high. Compressed air was blown over fifteen minutes into the molten bath, at a rate of cubic feet per minute. The temperature of the molten ferrophos withdrawn was measured at the outlet as 1325 C. by an optical pyrometer. It was controlled at this temperature by addition of residual ferrophos from the process in the amount of 10% of the original charge. A material having a specic gravity of 3.46, lower than that of the .ferrophos feed which was 5.2, formed and rose to the top of the ferrophos, and was removed by skimming from the converter. The residual ferrophos, having a specific gravity of 6.19, was drained out of the converter in an amount of 326 pounds, and found to contain 25.3% of phosphorus, 69.8% of iron, 1.16% of vanadium, and 1.3% of chromium. The concentrate was obtained in the amount of 149 pounds, and contained 10.5% of vanadium, 10.4% chromium, 19.6% of phosphorus, and 21.4% of iron. These percentage figures for the concentrate represent the percentages of the elements, not including their oxideoxygen. Only 8.6% of the original phosphorus was lost overhead from the process. The over-al1 yield of vanadium was 70.6% of the amount fed, while the ferrophos yield was 73.3%. The 25% phosphorus content of the residual ferrophos made the material directly useful in the production of high-phosphorus iron.

Example 2 PRESENT METHOD, CONTINUOUS PROCESS Two hundred pounds of ferrophos comprising 28.7% phosphorus, 4.9% vanadium, 4.8% chromium, 57.1% iron and 3% of calcium, was introduced into a Bessemer converter having a tap hole located for withdrawal of the vanadium concentrate, and having a tap hole near the bottom of the charge for withdrawal of the residual ferrophos. An entry port for introduction of air was located near the bottom of the converter, and a port for entry of ferrophos at the top of the converter.

The temperature of the charge was raised to ll C. by coke burned in the charge, and air was blown through the charge at a rate of 160 cubic feet per minute during the operation. This caused 4the temperature of the charge to rise to 1300 C., as measured by an optical pyrometer at the bottom tap hole. A concentrate formed and rose to the surface of the molten charge, and Was removed throughout the run through the upper tap hole.

Solid ferrophos was introduced into the top of the converter at a rate of 650 pounds per hour, and the concentrate removed at the rate of 338 pounds per hour. The temperature of the batch as measured at the bottom tapI hole, was maintained at about 1300 C. with the added solid ferrophos serving as a cooling agent. The residual ferrophos was periodically removed through the bottom tape hole to provide a proper level of reactants in the converter. It was removed at a rate of 447 pounds per hour.

The. residual ferrophos contained 1.46% of vanadium, 1.7% of chromium, 23.8% of phosphorus, and 66.5% of iron. The concentrate contained 6.7% of vanadium, 7.9% of chromium, 18.1% of phosphorus, and 22.5% of iron. Again the concentrate composition is given in terms of the contents of the elements themselves, not including oxide-oxygen. Only 8.8% of the phosphorus was lost.

AThe vanadium recovered in the concentrate was 70.5 of

the. amount fed, While the ferrophos yield was 68.7%.

Example 3 PRESENT METHOD, CONTINUOUS PROCESS 'When the process of Example 2 was repeated at a temperature at the bottom tap hole of 1400 C., With an airflow of 160 cubic feet per minute, the residual ferrophos was obtained at a rate of 410 pounds per hour, and the concentrate was recovered at a rate of 312 pounds per hour.

The ferrophos residual product contained 0.6% of chromium, 0.7% of vanadium, 25.3% of phosphorus, and 70.5% of iron. The concentrate contained 8.6% of vanadium, 8.5 of chromium, 17.0% of phosphorus, and 25.7% of iron. Only 16.2% of the phosphorus fed was lost. The vanadium obtained in the concentrate Was 90.5% of that fed, while the ferrophos yield was 63.3%.

Example 4 PRESENT METHOD, CONTINUOUS PROCESS The procedure of Example 2 was followed with the diierences that the temperature at the bottom tap hole during the reaction was maintained at about 1440 C., and the airflow through the reaction mixture was about 142 cubic feet per minute. Residual ferrophos was recovered at a rate of 355 pounds per hour, and concentrate was recovered a-t a rate of 307 pounds per hour.

The ferrophos residual contained 1.0% of vanadium, 0.9% of chromium, 24.2% of phosphorus, and 71.4% of iron. The concentrate contained 7.7% of vanadium, 8.5% of chromium, 16.1% of phosphorus, and 22.6% of iron. Phosphorus was lost only in the amount of 23.6%. The vanadium in the concentrate was 78.6% of the amount fed, while the yield of ferrophos was 54.6%.

, Example 5 PRIOR METHOD, NO TEMPERATURE CONTROL The procedure of Example 2 was followed, with the exception that no attempt was made to control the temperature of the reaction mass, with the ferrophos being introduced as molten material. In this case, the vanadium was substantially completely oxidized.

The temperature during the run rose toabout 1600 C. as measured at the bottom tap hole, and at this temperature excessive evolution of phosphorus Was observed. The phosphorus lost Was about 40% of the amount fed in the ferrophos, and the vanadium recovery in the concentrate Was 96% of the vanadium fed. The balance of the vanadium was substantially completely lost overhead.

The residual ferrophos product Was less than 30% of theory, and it contained only about 21% of phosphorus, of iron, 0.3% of vanadium, and 0.2% of chromium. The concentrate contained 3.3% of vanadium, 3.6% of chromium, 7.1% of phosphorus, and 28% of iron.

Example 6 PRESENT METHOD, LARGE BATCH Six tons of ferrophos comprising 28.7% phosphorus, 4.9% vanadium, 4.8% chromium, 57.1% iron and 3% calcium, was introduced over three hours into a Bessemer converter having a tap hole located near the bottom of the charge for removal of reaction mixture as required for continuous operation.

During addition of the charge, the temperature was maintained at about 1100 C. by burning coke beneath the charge. Thereafter, air was blown through the charge at a rate of about 900 cubic feet per minute during the operation. This caused the temperature of the charge, as measured at the tap hole with an optical pyrometer, to rise to and remain at about 1510 C. The reaction mixture in this case was turbulent, so that the concentrate and molten ferrophos mixture was removed intermittently at one-hour intervals through the bottom tap hole.

Solid ferrophos Was introduced into the top of the converter at the rate of four tons per hour, and the reaction mixture Was withdrawn in the amount of 41/2 tons per hour to maintain a relatively constant level of batch in the concentrate. The temperature of the batch, as measured at the tap hole with an optical pyrometer, was maintained at about 1510 C. by the added ferrophos, which served as a cooling means.

The withdrawn reaction mixture was permitted to cool in a quiescent state in a chill pit. While the material was still molten, the vanadium-rich concentrate rose to the surface and solidied over a gradually solidifying ferrophos base. When cool, the two layers were easily chipped apart.

The residual ferrophos contained 24.8% phosphorus, 0.94% vanadium, 0.95% chromium and 66.5% iron. The concentrate contained 8.1% vanadium, 8.2% chromium, 20.2% iron, and 14.1% phosphorus. The concentrate composition is given in terms of the elements therein, and not of their oxides. As indicated by the high phosphorus content of the residual ferrophos, very little phosphorus was lost.

It Will be seen from the above examples that by the vanadium and chromium concentration process of the present invention, ferrophos may be treated to provide a concentrate high in vanadium, and at the same time a residual ferrophos having a readily established and high phosphorus content of about 23% or more may be provided. This is in contrast to the method of they prior art, in which the temperature of reaction is not controlled, and While a concentrate having a high vanadium content is obtained, undetermined amounts of phosphorus are lost and a residual ferrophos having an undesirably low, and erratic, phosphorus content is produced.

Example 7 RECOVERY OF VANADIUM Seven tons of concentrate obtained by the method of Example 3, and containing 11.84% of V205, 10.22% of Cr2O3, 41.4% of P205 and 2.43% of CaO was ground in a ball mill with 25% of NaCl until 80% of the charge was 100 mesh. The mixture was then charged into a rotary kiln, heated to a temperature of 780 C., at a rate that gave a contact time of approximately 1 hour.

A gas containing HCl and Cl2 was treated in a scrubber with NH40H solution to provide a solution of ammonium chloride.

A sample of 300 pounds of calcine was taken from the discharge of the kiln when uniform feeding and discharge had been accomplished, and quenched in water. The quenched material was filtered and the solution and residue analyzed. The solution for precipitation contained 89.8 grams per liter of V205, 9 grams per liter of Cr205 and 1.4 grams per liter of P205. The washed and dried residue contained 4.27% V205. This residue was reroasted under similar conditions in the rst stage roast using 20% salt at a temperature of 780 C. for one hour. The operation of roasting was repeated on the leached calcine in the iirst stage roasting to increase recovery under identical conditions. The second treatment produced a calcine which when leached washed and dried contained 1.86% V205. The second residue was 90% of the weight of the first heads, giving a recovery in solution of 86% by the two-stage treatment. A third stage roast of the residue gave a final residue containing 0.90% V205, or a total recovery of 92.3% of the vanadium present in the concentrate.

The solutions, containing 72 grams of V205 per liter and less than 1 gram of P205 per liter, were treated for vanadium recovery by two methods.

The first method consisted in heating the solution to boiling and adding hydrochloric acid to a pH of 4. After boiling one hour, ammonium chloride Was added equivalent to l gram of ammonium chloride to 4 grams of V205 from the solution. A red precipitate was formed which was filtered, dried and analyzed. It contained 97.4% V205, 2.29% Na20, trace, less than 0.05%, P205 Iand trace Cr202. The filtrate contained 0.2 gram per liter f V205.

Another portion of this solution was heated with 2 grams of NH4C1 per gram of V205. The resulting precipitated ammonium metavanadate was dried and fused. It contained 99.1% V205, trace P205, trace Cr205. The filtrate contained 0.2 gram of V205 per liter.

Recovery of vanadium from solution was 99.7%; from concentrates in a two-stage roast, 85.6%; and from concentrates in a three-stage roast, 92%.

Example 8 RECOVERY 0F VANADIUM As a further example of the application of the invention, ten pounds of the same vanadium-rich concentrate was ground in a ball mill with 50% of sodium chloride to a fineness exceeding 150 mesh. This material was then charged to a multiple hearth furnace and roasted for a period of one hour during which time the temperature was adjusted from 600 to 790 C. The roasted material was then quenched in Water, filtered, and the residue analyzed. This washed and dried residue contained 1.45% V205. The solution resulting from the filtration contained 68 grams of V205 per liter, and 15 grams of NaCl and 0.8 gram P205 per liter. The solution was then heated to boiling and sulfuric acid was added to a pH of 4. After boiling one hour, a red precipitate was formed which was dried and analyzed. It contained 89% V205, 6% Na20 and less than 0.01% P205. The filtrate contained 0.15 gram per liter of V205.

Example 9 PRIOR METHODS When a concentrate containing 10.6% of vanadium, 30.5% iron and 7.75% calcium oxide was roasted at 820 C. for two hours with 30% of sodium carbonate, 84% of the vanadium was converted to water-soluble form. Roasting with 30% of sodium chloride at 820 C. for two hours converted only 51% of the vanadium to water-soluble form.

The solution resulting from the sodium carbonate roast contained 5 grams per liter of P205 as sodium phosphate. Precipitation of vanadium from the solution as red cake recovered 76% of the vanadium, and the red cake contained 0.07% of phosphorus, an amount exceeding the tolerable limit.

This example shows that when a large amount of calcium is present in the concentrate, i.e., above about 5% as Ca0, a sodium chloride roast does not convert the vanadium to water-soluble form in an acceptable amount. When sodium carbonate is used, suliicient vanadium is solubilized but at the cost of co-solubilization of an excessive amount of phosphorus.

The controlled vanadium-isolation roasting process of the Ipresent invention, on the other hand, provides solubilization of substantially all of the vanadium, without solubilization of an undue amount of phosphorus.

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplitied in a manner so that it can be readily practiced by those skilled in the art, such exempliiication including what is considered to represent the best embodiment of :the invention. However, it should be clearly understood that, within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure, otherwise than as specifically described and exemplied herein.

What is claimed is:

l. Method of recovering vanadium and chromium from ferrophos containing 24 to 28% of phosphorus, 52 to 60% of iron, 31/2 to 8% of vanadium, and 2 to 6% of chromium in a concentrate rich in these elements, and leaving a residual ferrophos having a high phosphorus content, comprising passing oxygen through said ferrophos while said ferrophos is in heated, molten condition at a temperature maintained between 1300 to 1560o C. until a concentrate rich in vanadium and chromium is formed, and separating said concentrate from the residual ferrophos.

2. Method of claim 1 in which the molten ferrophos is heated in an oxidizing atmosphere at a temperature of l400 to l500 C.

3. Method of claim 1 `in which the residual ferrophos contains at least about 23% of phosphorus.

4. Method of selectively recovering vanadium from ferrophos containing 24 to 28% of phosphorus, 52 to 60% of iron, 31/2 to `8% of vanadium and 2 to 6% of chromium and leaving a residual ferrophos having a high phosphorus content, comprising passing oxygen through said ferrophos while said ferrophos is in heated, molten condition at a temperature maintained at 1300 to 1560 C. until a vanadium-rich concentrate containing less than 5% of calcium as calcium oxide is formed, separating said concentrate from the residual ferrophos, roasting said concentrate in an oxidizing atmosphere with sodium chloride for one to two hours and at 600 `to 800 C. until vanadium in the concentrate is converted to a watersoluble sodium vanadate, leaching said sodium vanadate from the treated concentrate with water, and separating the resulting solutions from the remaining portions of the treated concentrate, said solutions having a low phosphorus content.

5. Method of recovering vanadium from a vanadiumrich concentrate containing at least 1% of vanadium calculated as V205 derived from ferrophos containing 24 to 28% of phosphorus, 52 to 60% of iron. 31/2 to 8% of vanadium and 2 to 6% of chromium, said concentrate containing less than 5% of calcium as calcium oxide, comprising roasting the concentrate in an oxidizing atmosphere with sodium chloride at a temperature of 600 to 800 C. for one to two hours until a water-soluble sodium vanadate is formed, leaching said sodium vanadate from the treated concentrate with water, and separating the resulting solution from the residue of the treated lconcentrate to. provide a sodium vanadate solution containing less than 0.1% of phosphorus calculated as P205.

6. Method of claim 5 in which the temperature of the roast is 600 to 700 C.

7. Method of claim 5 in Which the ferrophos-derived concentrate and the sodium chloride are particulate in form, and have aparticle size at least as line as 60 mesh, and said concentrate contains 10 to 15% of vanadium calculated as V205, 8 to 12% of chromium calculated as Cr203, and about 40% of phosphorus calculated as P205.

8. Method of claim 1 in which said oxygen is introduced in air.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Hampel: Rare Metals Handbook, 1st Edition, Rein- 10 hold Publishing Co., New York, pages 578-592 (published 1954). 

5. METHOD OF RECOVERING VANDIUM FROM A VANADIUMRICH CONCENTRATE CONTAINING AT LEAST 1% OF VANADIUM CALCULATED AS V2O5 DERIVED FROM FERROPHOS CONTAINING 24 TO 28% OF PHOSPHORUS, 52 TO 60% OF IRON, 3 1/2 TO 8% OF VANADIUM AND 2 TO 6% OF CHROMIUM, SAID CONCENTRATE CONTAINING LESS THAN 5% OF CALCIUM AS CALCIUM OXIDE, COMPRISING ROASTING THE CONCENTRATE IN AN OXIDIZING ATMOSPHERE WITH SODIUM CHLORIDE AT A TEMPERATURE OF 600* TO 800*C. FOR ONE TO TWO HOURS UNTIL A WATER-SOLUBLE SODIUM VANADATE IS FORMED, LEACHING SAID SODIUM VANADATE FROM THE TREATED CONCENTRATE WITH WATER, AND SEPARATING THE RESULTING SOLUTION FROM THE RESIDUE OF THE TREATED CONCENTRATE TO PROVIDE A SODIUM VANADATE SOLUTION CONTAINING LESS THAN 0.1% OF PHOSPHORUS CALCULATED AS P205. 